The present invention relates to an apparatus for processing a glass substrate or a thin film formed on a glass substrate by etching, CVD or sputtering.
In production of liquid crystal displays, glass substrates are widely used, and the glass substrates for liquid crystal displays are irresistibly increasing in terms of mass-productivity and a cost reduction. Further, various circuits formed on a glass substrate are becoming finer and higher in an integration degree. A dry etching technique and chemical vapor deposition (CVD) and physical vapor deposition (PVD) methods as thin film forming methods, for realizing fine processing in production of liquid crystal displays, are also required to have far higher accuracy, and there have been proposed processes which are devised and refined with regard to gas chemistry, a plasma source, glass substrate temperature control or the like.
The production of the liquid crystal display includes various processes for treating various thin films formed on the glass substrate, such as an insulating film, a semiconductor film, an electrically conductive film, etc., by etching, CVD processing, sputtering and the like. Those various thin films formed on the glass substrate will be sometimes generically referred to as "base material". There is a growing recognition that in the above treatment processes, controlling, setting and managing the temperature of the base material are essential for improving the accuracy of processing the base material and the accuracy of treatment of the base material.
In etching treatment and CVD treatment, plasma treatment is carried out in many cases. In plasma treatment at a high temperature, heat is abundantly transmitted from plasma into the base material due to ion impact on the basic material in the etching treatment and due to irradiation of high-density plasma to the base material in the CVD treatment. As a result, in many cases, the base material is temperature-increased by approximately 40.degree. C. to 100.degree. C. or more as compared with a temperature of the base material has before the generation of plasma. In a process of heating the base material with a glass substrate supporting stage for supporting a glass substrate and carrying out the plasma treatment at a high temperature, therefore, the technique of preventing the influence of heat transmission from plasma to the base material and controlling the base material at a predetermined temperature with high accuracy are essential.
However, temperature control at high temperatures according to prior arts cannot be said to be satisfactory. In a conventional technique, it is naturally expected that the base material is temperature-increased to the above-described extent during the process treatment, and the glass substrate supporting stage is set at a lower temperature by taking the above temperature increase of the base material into account. And, since the process is proceeded with taking the temperature increase of the base material into account, many problems remain to be solved, that is, the process takes a longer time, a throughput is decreased and the reproducibility and controllability of the process decrease due to a large change in temperature.
As one means for overcoming the above problems, a method is conceivable in which a glass substrate is fixed to the glass substrate supporting stage by means of a mechanical clamp device. However, when the mechanical clamp device is used, an in-plane temperature of the glass substrate is non-uniform or it is difficult to suppress the influence of heat transmission from plasma into the base material since the contact between the glass substrate supporting stage and the glass substrate is poor, which consequently causes a problem that the properties and the thickness of the base material formed on the glass substrate fluctuate depending upon positions of the base material on the glass substrate or that the properties of the base material fluctuate in the thickness direction of the base material. Further, when the base material formed on the glass substrate is etched, there is caused another problem that the form of the etched base material fluctuates depending upon positions of the base material on the glass substrate.
As another means for overcoming the above problems, it is conceivable to mount an electrostatic chuck on the glass substrate supporting stage. For mounting the electrostatic chuck on the glass substrate supporting stage, how to junction the heated glass substrate supporting stage and a dielectric material constituting the electrostatic chuck is a big problem which remains to be solved. This problem prevents the practical use of the glass substrate supporting stage on which the electrostatic chuck is mounted. That is, the glass substrate supporting stage designed for heating the substrate at high temperatures is required to effectively transmit heat to the base material when the base material is fixed onto the glass substrate supporting stage by adsorption with the electrostatic chuck. The glass substrate supporting stage and the electrostatic chuck are required to be junctioned to each other in a good thermal conduction state.
Meanwhile, aluminum (Al) is used as a material for the glass substrate supporting stage of a glass substrate processing apparatus such as an etching apparatus, a CVD apparatus and a sputtering apparatus, from the viewpoints of its high thermal conductivity and an easiness in processing thereof. Aluminum has a linear thermal expansion coefficient of approximately 23.times.10.sup.-6 /K. Generally, a ceramic material is used as a dielectric material for the electrostatic chuck. When the glass substrate supporting stage and the electrostatic chuck are directly junctioned to each other, therefore, the following problem is caused. Due to a linear thermal expansion coefficient difference between a ceramic material constituting the electrostatic chuck and aluminum constituting the glass substrate supporting stage, the ceramic material is damaged, i.e., broken by heating and cooling the glass substrate supporting stage, which results in the destruction of the electrostatic chuck.
For this reason, it is general practice at present to fix the electrostatic chuck to the glass substrate supporting stage by screws or the like. In the above structure, however, the junction interface between the electrostatic chuck and the glass substrate supporting stage is heat-insulated under vacuum when the pressure in the glass substrate processing apparatus is decreased, so that the efficiency of heat exchange between the glass substrate supporting stage and the base material through the electrostatic chuck is downgraded. As a result, the base material suffers heat from plasma and is temperature-increased to a level higher than a predetermined temperature. When a base material is formed on a glass substrate, there is therefore caused a problem that the properties and the thickness of the base material formed on the glass substrate fluctuate depending upon positions of the base material on the glass substrate, or that the properties of the base material fluctuate in the thickness direction of the base material. When the base material formed on the glass substrate is etched, there is also caused a problem that the form of the etched base material fluctuates depending upon positions of the base material on the glass substrate.
When the conventional supporting stage having the electrostatic chuck constituted of a dielectric member is heated up to a high temperature, the dielectric member undergoes cracking due to a linear thermal expansion coefficient difference between the supporting stage and the dielectric member, and the electrostatic chuck does not function as such any longer. For example, JP-A-10-32239 discloses means for overcoming the above problem, or discloses a supporting stage having an electrostatic chuck which is manufactured by junctioning a ceramic sintered plate for the electrostatic chuck and a ceramic/aluminum composite plate. The ceramic sintered plate for the electrostatic chuck and the composite plate are junctioned to each other by soldering or brazing. When the above supporting stage is used, plasma etching with excellent temperature control at a high temperature can be carried out. However, when a glass substrate having a large area of 0.6 m.times.0.7 m, or a glass substrate having a large area of 1 m.times.1 m to be used in the future, is processed, it is very difficult to manufacture a large-area composite plate composed of ceramic and aluminum.